Role of anisotropy and refractive index in scattering and whiteness optimization

The ability to manipulate light–matter interaction to tailor the scattering properties of materials is crucial to many aspects of everyday life, from paints to lighting, and to many fundamental concepts in disordered photonics. Light transport and scattering in a granular disordered medium are dictated by the spatial distribution (structure factor) and the scattering properties (form factor and refractive index) of its building blocks. As yet, however, the importance of anisotropy in such systems has not been considered. Here, a systematic numerical survey that disentangles and quantifies the role of different kinds and degrees of anisotropy in scattering optimization is reported. It is shown that ensembles of uncorrelated, anisotropic particles with nematic ordering enables to increase by 20% the reflectance of low-refractive index media (n = 1.55), using only three-quarters of material compared to their isotropic counterpart. Additionally, these systems exhibit a whiteness comparable to conventionally used high-refractive index media, e.g., TiO2 (n = 2.60). Therefore, the findings not only provide an understanding of the role of anisotropy in scattering optimization, but they also showcase a novel strategy to replace inorganic white enhancers with sustainable and biocompatible products made of biopolymers. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei